1. Technical Field
Example embodiments of the present invention relates to a membrane-electrode assembly (MEA) including a guard gasket.
2. Description of the Related Art
A fuel cell is a kind of power generation system that converts chemical energy of fuel directly into electric energy. Since the electric energy is generated directly from a fuel cell without requiring an additional step such as combustion, the fuel cell has advantages in that it produces little environmental contaminants and it provides high heat efficiency. Fuel cells are classified into polymer electrolyte membrane fuel cells (PEMFC), phosphoric acid fuel cells (PAFC), molten carbonate fuel cells (MCFC) and solid oxide fuel cells (SOFC) depending on the kinds of the electrolytes used therein.
A fuel cell comprises a stack formed by stacking a plurality of single cells, wherein each single cell comprises an MEA including an electrolyte membrane, a catalyst layer and a gas diffusion layer, and sandwiched between seperators. Additionally, surface grooving on the seperators allows supply and discharge of hydrogen on one side, and supply and discharge of oxygen gas in air on the other side.
The fuel cell causes fuel such as hydrogen or methanol to react electrochemically with oxygen to convert the chemical energy of the fuel directly into electric energy. Unlike conventional thermal power generation systems, fuel cells undergo no Carnot cycles so that they show high power generation efficiency, emit little contaminants such as NOx and SOx, and generate no noises during their operation. Therefore, fuel cells have been regarded as the most prominent clean energy source for the next generation. Fuel cells are classified into PEMFC, PAFC, MCFC, SOFC, etc., depending on the kinds of the electrolytes used therein. Among those, PEMFC have a lower driving temperature as compared to other kinds of fuel cells while showing excellent power generation efficiency and realizing compact structures. Thus, it is believed that PEMFC are useful as power sources for electric vehicles, compact power generation systems, for example, for household applications, mobile or emergency power sources, military power sources, etc.
In general, a PEMFC has a penta-layer structure of collector/anode/polymer electrolyte membrane (PEM)/cathode/collector. Fuel such as hydrogen or methanol is supplied to the anode, while air or oxygen is supplied to the cathode. At the anode, the fuel is oxidized to generate protons and electrons. The protons move toward the cathode through the electrolyte membrane, while the electrons move toward the cathode through wires and loads forming an external circuit. The protons and electrons react with oxygen at the cathode to produce water, which, in turn, is discharged to the exterior of the fuel cell.
Both electrodes of the PEMFC are obtained by applying an ink comprising a catalyst for activating the redox reaction, a polymer electrolyte and a solvent onto carbon paper or carbon cloth to form a catalyst layer. An example of the catalyst that is currently used includes a platinum-based catalyst which is comprised of platinum or platinum/ruthenium alloy having high catalytic activity and supported on a carrier formed of carbon particles.
Particular examples of the PEM include fluorosulfonate ionomer membranes such as Nafion (available from DuPont Co.), Flemion (available from Asahi Glass Co., Ltd.), Asiplex (available from Asahi Chemical Co. Ltd.) and Dow XUS (available from Dow Chemical Co.); and inorganic acid-doped polybenzimidazole (PBI)-based PEMs.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.